AR Buffer Weight to Slow Down Ejection

2:30-3:00 ejection is ideal. AR bolts are far from fagile and take a long time to break with normal use.

You could slow rearward bolt velocity with a heavier buffer or a stronger spring. Are you using a carbine buffer tube or rifle?

I wouldn’t mess with it unless you are actually experiencing a malfunction, but if you want to tune the buffer weight you can just take your buffer apart and replace your original buffer weights with tungsten weights and tune it as you see fit.

https://pur-tungsten.com/product/tungsten-recoil-buffer-weights/

I confess I like an ejection pattern where the brass is landing at about 4 O'clock. I use 6.8 oz. buffers in my guns. They work just fine for me.

DMW1116 said:

I’m using a load of CFE 223 powder pushing a 77 grain Sierra Match King. The accuracy in my 20” barrel rifle is excellent. The issue is the ejection is between 2:30 and 3 o’clock position. This rifle has a front sight post gas block so it’s not adjustable. My understanding is a heavier buffer would slow down the bolt carrier and change the ejection pattern. The slower bcg saves wear and tear in the rifle as I understand it. Should I look for a heavier buffer to try to slow down the bcg? The load is a mid-range charge so I’m not pushing for max velocity.

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You didn't mention what buffer you're using now.

ClemY said:

I confess I like an ejection pattern where the brass is landing at about 4 O'clock. I use 6.8 oz. buffers in my guns. They work just fine for me.

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A 6.8 .oz buffer is a rifle length buffer ? 20" barrels do like rifle Buffers I think.

Gordon said:

A 6.8 .oz buffer is a rifle length buffer ? 20" barrels do like rifle Buffers I think.

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Rifle buffers are roughly 5 ozs.

2:30-3:00 sounds pretty good as is. 3:00 ejection is usually regarded as perfect, and it's best to favor slightly forward of that for reliability. A more powerful round will eject less than 3:00, and a hotter round will go above 3:00.

If that were mine, and I wanted to modify ejection, I’d try to reduce gas. RCA makes an adjustable gas key you might try. https://www.righttobear.com/rca-adjustable-gas-key-1ad-gky/#product-reviews

I’ve ordered many times from RTB and trust them for hassle-free shopping.

Skylerbone said:

I’ve ordered many times from RTB and trust them for hassle-free shopping.

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Ditto. And I’ll also comment on the top quality components that Rubber City makes. I buy my bolts directly from them.

@ClemY ard you shooting 10mm? I tried a T3 (5.4 oz) buffer on my 7.5” 5.56 with my standard .223 range rounds and it failed to cycle the bolt several times before I swapped back to my T2 (4.3 oz).

In all honesty there doesn’t appear to be anything wrong at present. Who’s kit did you build with, and is the buffer marked or otherwise described on their site with weight stats?

Hedge your bets, because MistWolf will tell you this is a sure thing; buy some new extra power Colt extractor springs and get one installed immediately.

It’s backwards thinking to tune an AR to achieve a certain ejection angle. Install the right buffer, action spring, extractor spring, gas drive and use the correct ammo for reliably functioning AR and let the ejection angle take care of itself.

Mine all eject into a small mesh bag as a courtesy to those on my right and a little gift to myself for not having to chase it. Couldn’t tell you what o’clock they might send it to.

Skylerbone said:

In all honesty there doesn’t appear to be anything wrong at present. Who’s kit did you build with, and is the buffer marked or otherwise described on their site with weight stats?

Hedge your bets, because MistWolf will tell you this is a sure thing; buy some new extra power Colt extractor springs and get one installed immediately.

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Appreciate your comments. The only reason I have become concerned is that after say 1000 rounds through the AR 15 (Aero upper and lower, everything else is misc.) it has started to eject from 3 o'clock to 1:30. Actually like it better now because my net catches them and they never fly into my neighbors space or behind me to the right on a bounce.

DMW1116 said:

It’s a PSA lower and A2 lower build kit paired with one of their FN 20” rifle length uppers.

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It has a rifle buffer. You don't need (or want) anything heavier than that for 5.56/223.

A 20 inch upper is much easier on extractor springs than 16" and shorter upper are. However, it's a PSA upper with PSA springs. If I were in your shoes, I'd replace the extractor spring with a Colt or Sprinco spring, then go shooting and not worry any further. 20 inch uppers are much easier on extractor springs than the shorter length upper, but PSA extractor springs are not good quality.

Or, you can just keep shooting until the extractor spring starts to fail. When the AR starts stove piping or exhibits bolts overs, you'll know it's time for a new spring.

It's possible that the 20 inch upper is over gassed (but I think that's unlikely). If so, a heavier buffer won't help. You'll need to address the over sized gas port.

DMW1116 said:

What is a bolt over?

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Bolt over base. Caused by weak extraction.


Bolt over base with unejected empty. Caused by weak extraction.


To get good ejection, the extractor must hold the case firmly against the ejector plunger to keep the ejector spring compressed. The weak spring lets the extractor slip from the cartridge rim and the ejector spring relaxes before the front of the case clears the ejection port.

The uncontrolled case gums up the works by slowing the carrier return speed and blocking the feed of the top round from the magazine. This throws off timing. Slow carrier speeds lets top round nose up too much before the mag lips releases it and the result is a bolt over base malfunction.

Bolt over base with no ejected case, jammed in, can also be caused by high cyclic speeds.

I built a 6.8 with 16" barrel, and was using an A1 stock and rifle buffer. Worked great, ejected 2 - 4 pm with various 6.8 loads. I later switched to a carbine stock, tube and buffer, and it constantly jammed up. I realized that bolt speed was greatly increased with the light buffer weight causing the round to be cycled so fast it didn't have time to escape the port. The bolt would rebound, with casing still attached and attempt to chamber the empty with the new round.

Added a tungsten weight kit to bring the buffer to an H3. It immediately returned to functioning correctly. No issues since.

In tuning buffer weight, it's better slightly heavy than too light. All it will do is slow the cyclic rate from the high speed 900 rpm to the better 600, giving enough time to eject and then feed correctly. In the OP's case, it aint broke, don't fix it. There are some who do use a heavier than rifle buffer - the 9mm blow back, as it's all there is to delay the action. No gas.

Crane is the contractor who sets up and modifies short barreled AR's for shipboarding etc and their recommendation with 10.5" barrels is up to H3 to slow the cyclic. It's almost unecessary with a 20" with rifle gas as the pressure is about 10k psi lower at that port than carbine. I've heard of other methods to control where the brass lands, one is clipping the ejector spring by one coil. For a range only rifle with close stations, prone shooting, it seems to have a following. But - they are attempting to eject closer to 1 than 4 to avoid hitting other competitors, and hoping the guy on their left is equally considerate.

Me, I bought the net bag to collect brass. It works. Tuning, as I have discovered, has it's pitfalls.

I’m another one who really hadn’t worried about where on the sundial the case flies to as long as it’s running as expected and nothing is hiccuping. Once (If?) that happens I guess I’ll start tuning.

I’ve shot a lot of Mini-14’s for work over the past few decades (soon we’ll be all swapped to AR’s). I must say that with a Mini-14 the case ejection pattern isn’t measured using time… it’s measured by area codes.

Good luck finding your rifles sweet spot .

Stay safe.

Tirod said:

Bolt over base with no ejected case, jammed in, can also be caused by high cyclic speeds.

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That’s because the higher cyclic speeds places greater stress on the extractor and extractor spring. When the decision was made to switch to a higher energy powder for the M16, they had to develop a stiffer extractor spring to deal with the increased stress place on the extractor.

When they developed the M4, they again increased the spring rate of the extractor spring because the M16 spring wasn’t up to dealing with the increased stress placed on the extractor.

I built a 6.8 with 16" barrel, and was using an A1 stock and rifle buffer. Worked great, ejected 2 - 4 pm with various 6.8 loads. I later switched to a carbine stock, tube and buffer, and it constantly jammed up. I realized that bolt speed was greatly increased with the light buffer weight causing the round to be cycled so fast it didn't have time to escape the port. The bolt would rebound, with casing still attached and attempt to chamber the empty with the new round.

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My guess is the combination of higher carrier speeds and the heavier case over stressed the extractor spring. When the carrier speeds was reduced, the stress on the extractor was reduced. I had a 5.56 10.5 upper that was grossly over gassed (gas port was over 0.80) with excessively high carrier speeds and after I replaced the extractor spring with a Colt spring, never gave me bolt overs.

However, I have very little experience with ARs in calibers other than 5.56/223, so my guess above could very well be off the mark. Being chambered for 6.8 does change things.

In tuning buffer weight, it's better slightly heavy than too light. All it will do is slow the cyclic rate from the high speed 900 rpm to the better 600, giving enough time to eject and then feed correctly. In the OP's case, it aint broke, don't fix it. There are some who do use a heavier than rifle buffer - the 9mm blow back, as it's all there is to delay the action. No gas.

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I agree with you about keeping cyclic rate to about 600rpm.

I’d like to again point out my recommendations about buffer weights, extractor springs etc are for ARs chambered for 5.56 and 223 Wylde and equivalent.